Online histogram monitoring: automatic flags/improved performance

Added

• infinite number of histograms per row
• automatic flags (2) : overflow and underflow/ error displayed as red/blue borders on concerned histograms
• configuration: it is possible to configure the web app directly from a configuration json file.
  • to create the default configuration file : python3 config_manager.py <path_to_create_the_file>
• improved performance of web page
• Tag search with wildcard matching
• Pagination layout to avoid too many histograms on a single "page"
• Download displayed histograms